Image signal processor

ABSTRACT

An image signal processor comprising an image signal receiver and a white balance processing block is provided. The image signal receiver receives an image signal. The image signal is generated by an imaging device when the imaging device captures an optical image of an object. The imaging device captures the optical image of the object through a photographic optical system. The photographic optical system has a focus optical system. The focus optical system focuses the optical image on a light receiving surface of the imaging device. The photographic optical system is housed in a lens unit with a detector. The detector finds an object distance based on a location of the focus optical system in the photographic optical system. The white balance processing block carries out a white balance process for the image signal, based on a photographing magnification of the photographic optical system, the object distance, and the light intensity of the optical image as the image signal is generated.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image signal processor that carriesout a white balance process on image signals generated by an imagingdevice.

2. Description of the Related Art

A digital camera, which carries out a white balance process on imagesignals generated when photographing, is known. Further, a digitalcamera, which has a number of photographing-modes adequate to varioussituations and which carries out the white balance process according toa photographing-mode set up by the user, is proposed.

SUMMARY OF THE INVENTION

However, for any user setting up a photographing-mode is troublesome.Further, it is problematic that the digital camera inadequately carriesout the white balance process if the photographing-mode, set up by auser, does not match the situation where the user takes a photo.

Therefore, an object of the present invention is to provide an imagesignal processor that carries out a white balance process adequate for apractical situation where a user takes a photo.

According to the present invention, an image signal processor comprisingan image signal receiver and a white balance processing block isprovided. The image signal receiver receives an image signal. The imagesignal is generated by an imaging device when the imaging devicecaptures an optical image of an object through a photographic opticalsystem. The photographic optical system has a focus optical system. Thefocus optical system focuses the optical image on a light receivingsurface of the imaging device. The photographic optical system is housedin a lens unit. The lens unit has a detector to find an object distance.The object distance is found based on a location of the focus opticalsystem in the photographic optical system. The white balance processingblock carries out a white balance process for the image signal. Thewhite balance process is carried out based on a photographingmagnification of the photographic optical system, the object distance,and light intensity of the optical image as the image signal isgenerated by the imaging device.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the present invention will be betterunderstood from the following description, with reference to theaccompanying drawings in which:

FIG. 1 is a block diagram showing the internal structure of a digitalcamera having an image signal processor of an embodiment of the presentinvention;

FIG. 2 is a block diagram showing the internal structure of an imagesignal processor;

FIG. 3 is a first correlation diagram between the converted colordifference signals and the add-up color difference signals;

FIG. 4 is a second correlation diagram between a number of light sourcesand the converted color difference signals;

FIG. 5 is a flowchart of a number of signal processes carried out by theimage signal processor;

FIG. 6 is a first flowchart to explain the subroutine for a calculationof the Rg and the Bg; and

FIG. 7 is a second flowchart to explain the subroutine for a calculationof the Rg and the Bg.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is described below with reference to theembodiment shown in the drawings.

In FIG. 1, a digital camera 10 comprises a lens unit 68, an imagingdevice 42 such as a CCD, an image signal processor 20, a systemcontroller 52, a monitor 48, and so on.

The photographic optical system 41, which is housed in the lens unit 68,is optically connected to the imaging device 42. Between thephotographic optical system 41 and the imaging device 42, a mirror 65and a shutter 66 are mounted. The mirror 65 and the shutter 66 open fortaking a photo. Then, an optical image of an object through thephotographic optical system 41 is captured by a light 5 receivingsurface of the imaging device 42.

A plurality of pixels is arranged at a light receiving surface of theimaging device 42 in a matrix. Each pixel is covered by one color filterelement of the R (red) ,G (green), and B (blue) color filter elements(not depicted). Each pixel generates a pixel signal according to anamount of light received at each pixel. Pixel signals, generated by aplurality of pixels that accord to one frame of the photographed image,form the image signal. The image signal is output from the imagingdevice 42.

The image signal output from the imaging device 42 is sent to a CDS/AGCcircuit 43. The CDS/AGC circuit carries out correlated double samplingand auto gain control for the image signal. Then, the image signal issent to an A/D converter 44. The A/D converter 44 converts the imagesignal, which is an analogue signal, to a digital signal. After A/Dconversion, the image signal is sent to the image signal processor 20.

The image signal sent to the image signal processor 20 is stored by animage memory 45, which is a work memory for signal processing. The imagesignal processor carries out some predetermined signal processes, suchas a white balance process described later, for the image signal storedin the image memory 45.

The image signal processor 20 is electrically connected to a monitordriver 47 through a monitor I/F 46. The image signal is sent to themonitor driver 47 from the image signal processor 20 after predeterminedsignal processes. The monitor driver 47 drives the monitor 48 so that animage, corresponding to the image signals sent to the monitor driver 47,is displayed on the monitor 48.

In addition, the image signal processor 20 can be electrically connectedto a memory card 51 through a card I/F 49 and a connector 50. The memorycard 51 can be connected to and disconnected from the connector 50 asnecessary. The image signal, sent from the image signal processor 20,can be stored on the memory card 51.

The digital signal processor 20 is electrically connected to the systemcontroller 52. The system controller 52 causes the image signalprocessor 20 to adequately carry out the signal processes. In addition,the system controller 52 causes the digital camera 10 to carry out somemovements arranged for the digital camera 10.

The system controller 52 is electrically connected to a power switch 53,a mode switch 54, an AE/AF switch 55, and a release switch 56. Byswitching the power switch 53 on or off, the digital camera 10 isswitched on or off. A number of photographing-modes according to somephotographing situations are set up for the digital camera 10. Bymanipulating the mode switch 54, one photographing-mode is selected fromthe photographing-modes already set up. By switching on the AE/AF switch55, a number of operations for an auto exposure and an auto focus arecarried out, described in detail as follows.

The system controller 52 is electrically connected to a photometrysensor 57 and an AF sensor 58. When the AE/AF switch 55 is switched on,the degree of light intensity of the object is measured by thephotometry sensor 57 and a defocusing distance of the photographicoptical system 41 is measured by the AF sensor 58. Data for the measureddegree of light intensity and defocusing distance are sent to the systemcontroller 52.

Incidentally, an optical image of an object passing through thephotographic optical system 41 is reflected by a half mirror (notdepicted) mounted in the mirror 65 when the mirror 65 is closed. Then,the optical image of the object is incident to the AF sensor 58. The AFsensor is located so that the optical distance between the photographicoptical system 41 and the AF sensor 58, when closing the mirror 65, canbe equal to the optical distance between the photographic optical system41 and the imaging device 42.

The photographic optical system 41 comprises a number of lenses forminga zooming optical system 41Z for adjustment of focal length and a focusoptical system 41F that focuses the optical image. The zooming opticalsystem 41Z and the focus optical system 41F are separately supported andmoved by a lens driving mechanism (not depicted), housed in the lensunit 68, along the optical axis of the photographic optical system 41.

The lens driving mechanism has a driving motor (not depicted) formovement of the optical systems 41Z, 41F, and a location detector 69.The driving motor and the location detector 69 are electricallyconnected to a lens driver 59. The relative locations of the zoomingoptical system 41Z and the focus optical system 41F in the photographicoptical system 41 are detected by the location detector 69. Data for therelative locations are sent to the lens driver 59. The relative locationof the focus optical system 41F is detected as the distance from astandard position. When the relative location of the focus opticalsystem 41F is the standard position, an optical image of an objectinfinitely far apart from the photographic optical system 41 can befocused on the light receiving surface of the imaging device 42.

The lens driver 59 is electrically connected to the system controller52. Based on the defocusing degree measured by the AF sensor 58, thesystem controller calculates a distance to move the focus optical system41F from the original location to a location-in-focus, where the opticalimage of an object is focused on the light receiving surface.

Data for the distance to move the focus optical system 41F is sent tothe lens driver 59. Then, the lens driver 59 causes the driving motor tomove the focus optical system 41F to the location-in-focus.

The location detector 69 is electrically connected to a lens memory 60,housed in the lens unit 68. The lens memory 60 stores a firsttable-data, which has data for the relative location of the focusoptical system 41F and for the object distance corresponding to therelative location. Based on the actual relative location of the focusoptical system 41F and the first table-data, the lens memory 60 findsthe object distance corresponding to the actual relative location of thefocus optical system 41F. The object distance is sent to the systemcontroller 52 as a distance-information.

Further, the lens memory 60 stores a second table-data, which has datafor the relative location of the zooming optical system 41Z and for thefocal length corresponding to the relative location. Based on the actualrelative location of the zooming optical system 41Z and the secondtable-data, the lens memory 60 finds the focal length corresponding tothe actual relative location of the zooming optical system 41Z. Thefocal length is sent to the system controller 52 asfocal-length-information.

A diaphragm 61 is mounted between the zooming optical system 41Z and thefocus optical system 41F. An aperture ratio of the diaphragm 61 iscontrolled by the diaphragm driver 62.

The diaphragm driver 62 is electrically connected to the systemcontroller 52. Data for the degree of light intensity measured by thephotometry sensor 57 is sent to the diaphragm driver 62 through thesystem controller 52. Based on the degree of light intensity, thediaphragm driver 62 determines the aperture ratio of the diaphragm 61.

The system controller 52 is electrically connected to a mirror driver 63and a shutter driver 64. By switching on the release switch 56, thesystem controller 52 controls the mirror driver 63 and the shutterdriver 64 so that the mirror 65 and the shutter 66 can open.

In addition, by switching on the release switch 56, the systemcontroller 52 controls an imaging device driver 67 so that the imagingdevice 42 can generate one frame of the image signal.

Also, by switching on the release switch 56, the distance-information,the focal-length-information, and the light-amount-informationcorresponding to the measured amount of light intensity, when theimaging device generates the image signal, are sent to the image signalprocessor 20 from the system controller 52.

Next, the structure of the image signal processor is explained using theblock diagram showing the internal structure of the image signalprocessor (see FIG. 2). The image signal processor 20 comprises an I/Finput block 21, a color separation block 22, a white balance block 23, again calculation block 24, a color correction block 25, a gammacorrection block 26, a YC process block 27, an edge enhancement block28, a color signal block 29, and an I/F output block 30.

The image signal, which is converted to a digital signal by the A/Dconverter 44, is input to the I/F input block 21. The image signal issent to the image memory 45 from the I/F input block 21, and then theimage memory 45 stores the image signal. The image signal stored by theimage memory 45 is read by the color separation block 22. The imagesignal is separated into an R signal, a G signal, and a B signal,corresponding to red, green, and blue light components respectively.

The R signal, the G signal, and the B signal are input to the whitebalance block 23. Further, the white balance block 23 receives data foran R gain (hereinafter referred to as an Rg) and for a B gain(hereinafter referred to as a Bg), described in detail later, from thegain calculation block 24. Based on the Rg and the Bg, a white balanceprocess for the R signal, the G signal, and the B signal is carried out.

The R signal, the G signal, and the B signal, for which the whitebalance process is carried out, are sent to the color correction block25, and then a color correction process is carried out for them. The Rsignal, the G signal, and the B signal, for which the color correctionprocess is carried out, are sent to the gamma correction block 26, andthen a gamma correction process is carried out for them. The R signal,the G signal, and the B signal, for which the gamma correction processis carried out, are sent to the YC process block 27, and then aluminance signal (hereinafter referred to as Y) and color differencesignals (hereinafter referred to as Cr and Cb) are generated based onthe R signal, the G signal, and the B signal.

The Y is sent to the edge enhancement block 28, and then an edgeenhancement process is carried out for the Y. The Y, for which the edgeenhancement process is carried out, is stored by the image memory 45.The Cr and Cb are sent to the color signal block 29, and then a colorsignal process is carried out for the Cr and Cb. The Cr and Cb, forwhich the color signal process is carried out, are stored by the imagememory 45.

The Y, the Cr, and the Cb, stored by the image memory, are sent to themonitor I/F 46 or the card I/F 49 through the I/F output block 30.

Next, it is explained how the gain calculation block 24 calculates theRg and the Bg for the white balance process.

The image signal, which is converted to a digital signal by the A/Dconverter 44, is also input to the gain calculation block 24. The gaincalculation block 24 carries out a color separation process, an add-upprocess, and a YC process for the image signal, and then anadd-up-luminance signal (hereinafter referred to as aY) and add-up-colordifference signals (hereinafter referred to as aCr and aCb) aregenerated. Further, the gain calculation block 24 carries out a gaincalculation process based on the aY, the aCr, and the aCb, and then theRg and the Bg are calculated.

The color separation process, the add-up process, the YC process, andthe gain calculation process carried out by the gain calculation block24 are explained below in detail.

By carrying out the color separation process, the image signal isseparated into an R signal, a G signal, and a B signal in the same wayas in the color separation block 22. Each of the numbers of R signals, Gsignals, and B signals is equal to the number of pixels arranged in theimaging device 42.

For the add-up process, some add-up areas are set up on the lightreceiving surface of the imaging device 42. For example, the lightreceiving surface is divided vertically into 16 areas and horizontallyinto 16 areas, and thus 256 add-up areas are formed. More than 16 pixelsare vertically and horizontally arranged on the light receiving surface.In addition, each add-up area includes a number of pixels. An R add-upvalue is calculated by adding up signal levels of the R signalsgenerated by the pixels included in a single add-up area. Similarly, a Gadd-up value is calculated by adding up signal levels of the G signalsgenerated by the pixels included in a single add-up area. Similarly, a Badd-up value is calculated by adding up signal levels of the B signalsgenerated by the pixels included in a single add-up area. The R add-upvalue, the G add-up value, and the B add-up value are calculated foreach of the 256 add-up areas.

By carrying out the YC process, the aY, the aCr, and the aCb aregenerated based on the R add-up values, the G add-up values, and the Badd-up values. The Y, the Cr, and the Cb are generated for each pixel inthe YC process block 27, but the aY, the aCr, and the aCb are generatedfor each of the 256 add-up areas in the gain calculation block 24.

Initially in the gain calculation process next to the YC process, theaCr and the aCb are converted into converted color difference signals(hereinafter referred to as cCr and cCb) , corresponding to a standardluminance signal (hereinafter referred to as sY). The signal level ofthe sY is predetermined, and can be set, for example, to a median signallevel in the detectable signal level range for the aY.

The conversion to the cCr and the cCb is explained below using the firstcorrelation diagram of FIG. 3. FIG. 3 is a first correlation diagram,with the cCr and the cCb corresponding to the sY, and the aCr, and theaCb corresponding to the aY, respectively. The first correlation diagramis described in a three-dimensional coordinate space, with one axis ofY, and two axes of Cr and Cb. The signal levels of the Y, the Cr, andthe Cb are all zero at the origin of the coordinates in FIG. 3.

As described before, the aY, the aCr, and the aCb are calculated foreach add-up area. For a first add-up area, the origin and a first pointare connected by a first straight line. The coordinates of the Y, theCr, and the Cb at the first point are, respectively, aY1, aCr1, and aCb1There is a first intersection point of the first straight line and astandard-plane, where the coordinate of the luminance signal is sY. Thecoordinates of the Cr and the Cb at the first intersection point are,respectively cCr1 and cCb1. Similarly, the aCrs and the aCbs for all theadd-up areas are converted into cCrs and cCbs.

The gain calculation block 24 receives the distance-information and thefocal-length-information, when the imaging device generates an imagesignal, from the system controller 52. The gain calculation block 24makes an approximate calculation of a photographing magnification bydividing the focal length corresponding to the focal-length-informationby the object distance corresponding to the distance-information.

Further, the gain calculation block 24 receives thelight-amount-information as an apex conversion value for the lightamount (hereinafter referred to as Lv) from the system controller 52.

The Rg and the Bg are calculated based on the cCr and the cCb, thephotographing magnification, the object distance, and the Lv.

Initially, in order to calculate the Rg and the Bg, the gain calculationblock 24 predicts actual light source illuminating the object. Themethod for predicting the type of the actual light source is explainedbelow using the second correlation diagram of FIG. 4. The secondcorrelation diagram is described in a two dimensional coordinate plain,which has the two axes of cCr and cCb.

Sunlight in a sunny place in fine weather, sunlight in a sunny place incloudy weather, sunlight in the shade in fine weather, an incandescentlight, and a fluorescent light are set up as hypothetical light sourcesfor predicting. The light sources, of which the color temperatures are4000K˜5500K, 5500K˜7000K, and 7000K˜9000K, are respectively defined assunlight in a sunny place in fine weather, sunlight in a sunny place incloudy weather, and sunlight in the shade in fine weather. In the twodimensional coordinate plain having the two axes of cCr and cCb, somepredicting-areas are predetermined. Each of the predicting-areascorresponds to one of the light sources.

When an actual light source is a fluorescent light, many of theintersection points are included in a first predicting-area. When anactual light source is sunlight in a sunny place in fine weather, manyof the intersection points are included in a second predicting-area.When an actual light source is sunlight in a sunny place in cloudyweather, many of the intersection points are included in a thirdpredicting-area. When an actual light source is sunlight in the shade infine weather, many of the intersection points are included in a fourthpredicting-area. When an actual light source is an incandescent light,many of the intersection points are included in a fifth predicting-area.

For predicting the light source, it is determined which predicting-areaincludes which color-points, where coordinates of one color differencesignal and the other color difference signal are the cCr and the cCb ofeach add-up area. The cCr and the cCb, of which the color-points are notincluded in any predicting-areas, are excluded from predicting theactual light source.

A light source, corresponding to a predicting-area which includes themost color-points, is predicted as an actual light source, except forthe specific cases described later. The cCrs and the cCbs of thecolor-points, included in the predicting-area corresponding to thepredicted actual light source, are selected for a calculation of the Rg,and the Bg. The other cCrs/cCbs are excluded from the calculation.

Then, the average values of the selected cCrs/cCbs are calculated. Next,the sY and the average values of the selected cCrs and cCbs areconverted into R signal, G signal, and B signal, The Rg is calculated bydividing the G signal by the R signal and the Bg is calculated bydividing the G signal by the B signal. As described before, data for theRg and the Bg are sent to the white balance block 23.

Next, the specific cases for predicting the light source are explainedbelow.

If the object distance is over a first distance, the firstpredicting-area is excluded from predicting the actual light source. Thefirst distance is a predetermined distance, which can be considered asinfinite for the photographic optical system. For example, the firstdistance can be predetermined to be 10 meters.

If the object distance is less than the first distance and greater thana second distance and the photographing magnification is over apredetermined magnification, the first predicting-area is excluded fromis predicting the light source. For example, the second distance can bepredetermined to be 8 meters, and the predetermined magnification can be8.

By excluding the first predicting-area, a light source, corresponding toa predicting-area that includes the second most color-points, is thenpredicted as the actual light source, even if the first predicting-areaincludes the most color points.

If the Lv is over 12 in addition to excluding the first predicting-area,the fourth and the fifth predicting-areas are also excluded frompredicting the actual light source. By excluding the first, the fourth,and the fifth predicting-areas, a light source, corresponding to eitherthe second or the third predicting-area (whichever includes morecolor-points) , is predicted as the actual light source.

After predicting the actual light source, the Rg and the Bg arecalculated as described above. If the Lv is over 14, the Rg and the Bgare set up to be 1 even if the predicting-area includes the mostcolor-points. Data for the Rg and the Bg are sent to the white balanceblock 23.

Next, some movements carried out by the digital camera are explainedusing the flowcharts of FIG. 5˜FIG. 7.

In FIG. 5, at step S100, it is determined whether the release switch 56is switched on or not. If the release switch is switched off, theprocess goes to step S101. At step S101, it is determined whether theAE/AF switch 55 is switched on or not. If the AE/AF switch 55 isswitched off, all operations of the digital camera 10 finish. If theAE/AF switch 55 is switched on, the process returns to step S100.

If the release switch is switched on at step S100, the process goes tostep S102. At step S102, some necessary operations for release arecarried out, and then the mirror 65 and the shutter 66 are opened, andthe imaging device 42 is driven, so that imaging device generates animage signal.

After the operations for release are carried out, the process goes tostep S103. At step S103, the correlated double sampling and the autogain control process are carried out for the image signal. Further, A/Dconversion is carried out for the image signal. After the A/Dconversion, the image signal processor 20 reads the image signal. Atstep S104, the image signal is stored by the image memory 45. Theprocess goes to step S200 after step S104. At step S200, the Rg and theBg are calculated, as described below in detail.

The process goes to step S105 after calculation of the Rg and the Bg. Atstep S105, the white balance process is carried out using the calculatedRg and Bg. In this white balance process, first, the color separationprocess is carried out for the image signal stored by the image memory45, and then the image signal is separated into the R signals, the Gsignals, and the B signals. Second, the R and the B signals aremultiplied, by the Rg and the Bg respectively. Then the white balanceprocess is completed.

The process goes to step S106, where the color correction process iscarried out after the white balance process. Then, the gamma correctionprocess is carried out at step S107 after the color correction process.Next, the YC process is carried out for the R signal, the G signals, andthe B signals at step S108 after the gamma correction process, and thenthe image signal formed by the R, the G, and the B signal components areconverted into the image signal formed by the Y, the Cr, and the Cb.

The process goes to step S109 after step S108. At step S109, the edgeenhancement process is carried out for the Y, and the color signalprocess is carried out for the Cr and the Cb. At step S110, the Y, forwhich the edge enhancement process is carried out, and the Cr and theCb, for which the color signal process is carried out, are stored by theimage memory 45. After storing the Y and the Cr/Cb, all operations ofthe digital camera 10 finish.

Next, the subroutine for calculation of the Rg and the Bg at the gaincalculation block 24 is explained below in detail.

In FIG. 6, the process at step S201 continues after finishing theprocess of step S104. At step S201, the gain calculation block 24 readsthe image signal, the distance-information, thefocal-length-information, and the light-amount-information.

At step S202, the color separation process is carried out for the imagesignal, and then the R signal, the G signal, and the B signal, which arecomponents of the image signal, are separated.

At step S203, the add-up process is carried out for the R signal, the Gsignal, and the B signal that are separated at step S202, and then the Radd-up value, the G add-up value, and the G add-up value are calculated.

At step S204, the aY, the aCr, and the aCb are generated based on the Radd-up value, the G add-up value, and the B add-up value. At step S205,the aCr and the aCb are converted into the cCr and the cCb.

At step S206, it is determined whether the Lv is over 14 or not. If theLv is over 14, the process goes to step S207. At step S207, the Rg andthe Bg are set to 1. The white balance process is unnecessary if the Lvis over 14. The Rg and the Bg set to 1, a value that corresponds toskipping the virtual white balance, are used for the white balanceprocess at step S105.

The process goes to step S208 when the Lv is not over 14 at step S206.At step S208, it is determined whether the object distance is greaterthan the first distance, which can be considered infinite. If the objectdistance is greater than the first distance, the process goes to stepS212. Fluorescent light is excluded when predicting the actual lightsource at all steps after step S212, to be described later. The reasonfor this exclusion is that it can be judged that the object is out ofdoors if the object distance is infinite.

If the object distance is not greater than the first distance at stepS208, the process goes to step S209. At step S209 and step S210, it isdetermined whether the photographing magnification is greater than thepredetermined magnification, and whether the object distance is greaterthan the second distance, respectively. If the photographingmagnification is greater than the predetermined magnification and theobject distance is greater than the second distance, the process goes tostep S212.

If the photographing magnification is not greater than the predeterminedmagnification or the object distance is not greater than the seconddistance, the process goes to step S211. At step S211, allpredicting-areas are selected to predict the actual light source.

At step S212, it is determined whether the Lv is greater than 12. If theLv is greater than 12, the process goes to step S213, and then thesecond and the third predicting-areas are selected to predict the actuallight source. The Lv is considered greater than 12 if the actual lightsource is sunlight in a sunny place in fine weather or sunlight in asunny place in cloudy weather. Consequently, the selection of thepredicting-areas at step S213 is appropriate.

When the Lv is not greater than 12 at step S212, the process goes tostep S214. At step S214, all predicting-areas, excluding the firstpredicting-area, are selected to predict the actual light source.

The process goes to step S215 after step S211, step S213, or step S214finishes. At step S215, the predicting-area that includes the mostcolor-points is detected from among the selected predicting-areas atstep S211, step S213, or step S214. The actual light source isidentified by detecting the predicting-area.

The process goes to step S216 after identification of the actual lightsource. At step S216, the average value of the cCrs/cCbs, of whichcolor-points are included in the identified predicting-area at stepS215, is calculated.

The process goes to step S217 after the calculation. At step S217, thesY and the average values calculated at step S216 are converted into anR signal, a G signal, and a B signal. At step S218, the Rg is calculatedby dividing the R signal by the G signal. Further, at step S218, the Bgis calculated by dividing the B signal by the G signal.

The subroutine finishes after calculating the Rg and the Bg, and thenthe process goes to step S105 as described before.

In the above embodiment, it is possible to carry out an adequate whitebalance without user intervention for setting up a photographing-mode.Further, an adequate white balance can be carried out even if the usersets up a photographing-mode inadequate to the condition where aphotograph is taken.

When an object mostly colored green is photographed outside in sunnyweather, a white balance for an object illuminated by fluorescent lightmay be carried out according to a method of white balance in prior art.However, it is possible to prevent inadequate white balance even undersuch conditions in the above embodiment.

The first distance is set at 10 meters in the above embodiment. However,any distances are adaptable as long as the photographing location can beconsidered outside. Further, the second distance and the predeterminedmagnification are set at 8 meters and 8, respectively in the aboveembodiment. However, the combination of the second distance and thephotographing magnification is adaptable as long as the photographinglocation can be considered outside.

A specific light source can be excluded from predicting the actual lightsource based on the object distance and the photographing magnification.However, the exclusion may be carried out based on either the objectdistance or the photographing magnification by itself.

A defocusing distance of the photographic optical system 41 is measuredby the AF sensor 58 in the above embodiment. However, the defocus amountcan be measured by the imaging device 42. For instance, in a compactcamera where the imaging device always receives an optical image, thissetting is applicable.

Furthermore, in the above embodiment, the focus optical system 41F ismoved a distance based on the defocusing distance detected by the AFsensor 58, and then the object distance is detected based on the newlocation of the focus optical system 41F. However, the object distancemay be directly measured by a range-finding sensor as well.

The add-up process is carried out by the gain calculation block 24 inthe above embodiment. However, an adequate white balance can be carriedout without the add-up process. Nevertheless, it is desirable to carryout the add-up process because it facilitates a quick calculation of theRg and the Bg. In addition, the carrying out of the add-up process doesnot present any problems, since adequate Rg and Bg are still calculated.

Although the embodiments of the present invention have been describedherein with reference to the accompanying drawings, obviously manymodifications and changes may be made by those skilled in this artwithout departing from the scope of the invention.

The present disclosure relates to subject matter contained in JapanesePatent Application No. 2005-193944(filed on Jul. 1, 2005), which isexpressly incorporated herein, by reference, in its entirety.

1. An image signal processor, comprising: an image signal receiver thatreceives an image signal generated by an imaging device when saidimaging device captures an optical image of an object through aphotographic optical system, the photographic optical system having afocus optical system that focuses said optical image on a lightreceiving surface of said imaging device, and the photographic systembeing housed in a lens unit having a detector to find an object distancebased on a location of said focus optical system in said photographicoptical system; and a white balance processing block that carries out awhite balance process for said image signal, based on a photographingmagnification of said photographic optical system, said object distance,and light intensity of said optical image as said image signal isgenerated by said imaging device.
 2. An image signal processor accordingto claim 1, wherein said photographing magnification is calculated basedon said object distance and focal length of said photographic opticalsystem.
 3. An image signal processor according to claim 1, wherein saidphotographic optical system has a zooming optical system used foradjustment of focal length of said photographic optical system.
 4. Animage signal processor according to claim 1, further comprising a colorseparation block, which separates said image signal into primary colorsignal components for each picture element forming a light receivingsurface of said imaging device, and a signal conversion block, whichconverts said primary color signal components into first and secondcolor difference signals; and said white balance processing blockcalculating a white balance gain used for multiplying said image signal,based on average values of said first color difference signals of saidpicture elements and said second color difference signals of saidpicture elements, and carrying out said white balance process for saidimage signal with said white balance gain.
 5. An image signal processoraccording to claim 4, wherein a number of predicting-areas, on a twodimensional coordinate plain of said first and said second colordifference signals, are predetermined for predicting an actual lightsource illuminating said object, and said white balance processing blockcalculates said white balance gain, based on average values of saidfirst and said second color difference signals whose color combinationfor said picture elements are included only in said predicting-area thatincludes the most of said color combinations.
 6. An image signalprocessor according to claim 4, wherein a number of predicting-areas, ona two dimensional coordinate plain of said first and said second colordifference signals, are predetermined for predicting an actual lightsource illuminating said object, and said predicting-areas comprise afirst predicting-area, corresponding to a first light source, and asecond predicting-area, corresponding to a second light source, and saidwhite balance processing block calculates said white balance gain, basedon average values of said first and said second color difference signalswhose color combination for said picture elements are included only insaid predicting-area that includes the most of said color combinationsexcept for said first and said second predicting-areas, if said objectdistance is over a first distance and said light intensity of saidoptical image is over a predetermined intensity; or if said objectdistance is between a range of said first distance and a second distancebeing shorter than said fist distance, said photographing magnificationis over a predetermined magnification, and said light intensity of saidoptical image is over said predetermined intensity.
 7. An image signalprocessor according to claim 6, wherein said white balance processingblock calculates said white balance gain, based on average values ofsaid first and said second color difference signals whose colorcombination for said picture elements are included only in saidpredicting-area that includes the most of said color combinations exceptfor said first predicting-area, if said object distance is greater thansaid first distance and said light intensity of said optical image isless than said predetermined intensity, or if said object distance isbetween a range of said first distance and said second distance, saidphotographing magnification is greater than a predeterminedmagnification, and said light intensity of said optical image is lessthan said predetermined intensity.
 8. An image signal processoraccording to claim 6, wherein said white balance processing blockcalculates said white balance gain, based on average values of saidfirst and said second color difference signals whose color combinationfor said picture elements are included only in said predicting-area thatincludes the most of said color combinations, if said photographingmagnification is less than said predetermined magnification, or if saidphotographing magnification is greater than said predeterminedmagnification and said object distance is less than said seconddistance.
 9. An image signal processor according to claim 6, whereinsaid first light source is predetermined to be a fluorescent light. 10.An image signal processor according to claim 6, wherein said secondlight source is predetermined to be sunlight in the shade in fineweather or an incandescent light.